1. Field of the Invention
The present invention relates to an image display device capable of high-quality color display and, more particularly, to an image display device that can be downsized, using pixel drive electronics circuitry built into a compact package area.
2. Description of the Related Art
Referring to FIG. 15, a typical prior-art display device is described below.
In recent years, studies of so-called organic electroluminescent (EL) displays using organic EL (also referred to as Organic Light Emitting Diode (OLED) elements have been vigorously pursued. However, if the aim of the organic EL display method is light emission in full colors and tones, ideally, all organic EL elements corresponding to R, G, and B colors of light emission must carry separate drive currents to represent tones in order to obtain given luminance with given chromaticity because the organic EL elements for R, G, and B have different optical light emission characteristics. In consequence, when driving the R, G, and B pixels simply by a single drive circuit, like the drive circuit for conventional liquid crystal displays, the problem arises that desired colors cannot be reproduced or the tones are hard to control.
FIG. 15 is a diagram representing a schematic circuitry structure of a simple-matrix-type organic EL display which has been proposed to avoid the above problem.
On the substrate 201, organic EL elements 202 are arranged in a matrix and connected to a plurality of data lines 203. R, G, and B organic EL elements 202 are connected to corresponding R, G, and B data lines 203. The R, G, and B data lines 203 on one end thereof are connected to corresponding R, G, and B tap electrodes 204. The R, G, and B tap electrodes 204 are connected to organic EL drive circuits for R, G, and B colors, respectively, via the lines reconnection means 205. The lines reconnection means 205 is a multilevel interconnection board built, using a plastic-molded multilayer buildup substrate, and having the duty of connecting the R, G, and B tap electrodes 204 to the organic EL drive circuits 206 for R, G, and B colors.
The operation of this example of a prior-art display device is next briefly described. When a row of organic EL elements 202 that will be driven to emit light is selected by a scan-by-the-row circuit (not shown), corresponding pixel data signals are input from the organic EL drive circuits 206 through the data lines 203 to the organic EL elements 202 in the row. Then, the organic EL elements 202 in the selected row emit light, according to the pixel data signals. In this way, scanning each row and inputting pixel data signals to the organic EL elements in the row are repeated and thereby the organic EL display presents an image. In this prior-art display device, the introduction of the lines reconnection means 205 makes it possible to drive the R, G, and B organic EL elements separately by the organic EL drive circuits 206 for R, G, and B colors and the above-noted problem can be avoided. JP-A No. 56732/2000 describes the above prior-art display device in detail.
In the sphere of small and medium size crystal displays, a technique for building an analog signal drive circuit using polycrystalline Si-TFTs (Thin Film Transistors) together with pixels on a same glass substrate is now being developed. This technique is expected to reduce the cost of the analog signal drive circuit and improve the impact-resistant reliability of the display. In such technique, the analog signal drive circuit comprises shift registers, latch circuits, D-A converter, and other circuits. This technique is described in detail in, for example, Proceedings of 2000 IEEE International Solid-State Circuits Conference (ISSCC 2000), pp. 188-189.
If the organic EL display can be constructed by building the above-mentioned prior art analog signal drive circuit using polycrystalline Si-TFTs together with pixels on the same glass substrate, cost reduction and improved impact-resistant reliability of the display would be expected similarly. For the organic EL display, however, ideally, it is necessary to supply separate drive currents to represent tones to the organic EL elements of R, G, and B colors, as noted above. Therefore, when building an analog signal drive circuitry on a glass substrate like the above-mentioned prior art liquid crystal displays, separate analog signal drive circuits for R, G, and B colors must be built. In consequence, even if the above-mentioned lines reconnection means is used, the area of the analog signal drive circuits becomes three times the corresponding area in the case of a liquid crystal display. This will be obstructive to downsizing the display device, taking the packaging area for the components of the organic EL display into consideration.
Although the above discussion assumed that the analog signal drive circuits using polycrystalline Si-TFTs are built together with pixels on the same glass substrate, even if these circuits are built, respectively, on monocrystalline LSIs, three drive circuit LSTs are mounted to the display. This is obviously disadvantageous in view of the packaging area and the same problem exists.